An important aspect of wireless or radio communications technology relates to mobility and/or access selection between cells of different radio access networks or between different cells of the same radio access network. When considering different radio access networks, the source cell and the target cell may belong to radio access networks of different radio access technologies such as a cellular network and a Wireless Local Area Network, WLAN.
Communication devices such as terminals are also known as e.g. User Equipments (UE), mobile terminals, wireless terminals and/or mobile stations. Terminals are enabled to communicate wirelessly in a cellular communications network or wireless communication system, sometimes also referred to as a cellular radio system or cellular networks. The communication may be performed e.g. between two terminals, between a terminal and a regular telephone and/or between a terminal and a server via a Radio Access Network (RAN) and possibly one or more core networks, comprised within and/or connected to the cellular communications network.
Examples of wireless communication systems are Long Term Evolution (LTE), Universal Mobile Telecommunications System (UMTS) and Global System for Mobile communications (GSM).
Terminals may further be referred to as mobile telephones, cellular telephones, laptops, or surf plates with wireless capability, just to mention some further examples. The terminals in the present context may be, for example, portable, pocket-storable, hand-held, computer-comprised, or vehicle-mounted mobile devices, enabled to communicate voice and/or data, via the RAN, with another entity, such as another terminal or a server.
The cellular communications network covers a geographical area which is divided into cell areas, wherein each cell area being served by an access node such as a base station, e.g. a Radio Base Station (RBS), which sometimes may be referred to as e.g. “eNB”, “eNodeB”, “NodeB”, “B node”, or BTS (Base Transceiver Station), depending on the technology and terminology used. The base stations may be of different classes such as e.g. macro eNodeB, home eNodeB or pico base station, based on transmission power and thereby also cell size. A cell is the geographical area where radio coverage is provided by the base station at a base station site. One base station, situated on the base station site, may serve one or several cells. Further, each base station may support one or several communication technologies. The base stations communicate over the air interface operating on radio frequencies with the terminals within range of the base stations. In the context of this disclosure, the expression Downlink (DL) is used for the transmission path from the base station to the mobile station. The expression Uplink (UL) is used for the transmission path in the opposite direction i.e. from the mobile station to the base station.
By way of example, in 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE), base stations, which may be referred to as eNodeBs or even eNBs, may be directly connected to one or more core networks.
3GPP LTE radio access standard has been written in order to support high bitrates and low latency both for uplink and downlink traffic. All data transmission in LTE is controlled by the radio base station.
As an example, Wi-Fi and similar WLAN technologies have been subject to increased interest from cellular network operators, not only as an extension to fixed broadband access. The interest is mainly about using the Wi-Fi technology as an extension, or alternative to cellular radio access network technologies to handle the always increasing wireless bandwidth demands. Cellular operators that are currently serving mobile users with, e.g., any of the 3GPP technologies, LTE, UMTS/WCDMA, or GSM, see Wi-Fi as a wireless technology that may provide good support in their regular cellular networks. The term “operator-controlled Wi-Fi” points to a Wi-Fi deployment that on some level is integrated with a cellular network operator's existing network and where the 3GPP radio access networks and the Wi-Fi wireless access may even be connected to the same core network and provide the same services.
There is currently some activity in the area of operator-controlled Wi-Fi in several standardization organizations. In 3GPP, activities to connect Wi-Fi access points to the 3GPP-specified core network is pursued, and in Wi-Fi Alliance (WFA) activities related to certification of Wi-Fi products are undertaken, which to some extent also is driven from the need to make Wi-Fi a viable wireless technology for cellular operators to support high bandwidth offerings in their networks. The term Wi-Fi offload is commonly used and points towards the situation that cellular network operators seek means to offload traffic from their cellular networks to Wi-Fi, e.g., in peak-traffic-hours and in situations when the cellular network for one reason or another needs to be off-loaded, e.g., to provide requested quality of service, maximize bandwidth or simply for coverage.
Most current Wi-Fi and current other Wireless Local Area Network (WLAN) deployments are totally separate from mobile networks, and may be seen as non-integrated from the terminal perspective. Most Operating Systems (OS) for UEs, such as Android™ and ioS®, support a simple Wi-Fi offloading mechanism where a UE immediately switches all its IP traffic to a Wi-Fi network upon a detection of a suitable network with a received signal strength above a certain level. Henceforth, the decision to offload to a Wi-Fi or not is referred to as access selection strategy and the term “Wi-Fi-if-coverage” is used to refer to the aforementioned strategy of selecting Wi-Fi whenever such a network is detected.
A problem is that a UE with a mobility policy implying offloading to a cell in another radio access network, or to a cell of the same radio access network may be “ping-ponged” back and forth between cells. This so-called ping-pong effect results in degraded performance of the UE and of the involved radio access network(s). For example, the ping-ponging may result in service interruptions as well as generate considerable unnecessary signalling.